USB RS-485 Adapter Through Hole PCBs Revisited

The second batch of through hole PCBs arrived recently.  I had fixed errors in the original design, moved some components around, corrected the silkscreen, and added silkscreen labels.  The design was uploaded to China, services paid for, and twelve PCBs were handed to me by the postal worker about four weeks later.

The worst offence of the original design was necessary green wire jumps and cuts rework for the Vcc and Vusb lines.  This new board doesn't require any rework.  I built up two boards and one works, and unfortunately I snipped a power line on the second board while trimming leads on a capacitor and some green wire solved the problem (oops, but good save!).

The silkscreen labels are a bit too small to see with my eyes, but make the board more usable.  I moved the JITE socket out so it hangs off the board with the benefit of the board also fitting screw terminals like those used in my (mostly) surface mount USB RS-485 Adapter board.

USB RS-485 Adapter Surface Mount Boards

The surface mount PCB version of my RS-485 adapter recently arrived from overseas.  This one is cheaper and cleaner using the 20-pin PIC18F14K50, mostly surface mount parts, and fewer LEDs.  These require more patience to build than the through hole version.

I like the expansion ports on this one.  They are Arduino-esque, with power rails opposite data rails, allowing good stability of possible shield expandability.  Every data pin, including the ones used for RS-485 are drawn out to pads. 

Jumpers are provided to choose whether to connect the RS-485 read enable and drive enable lines from PORTB or PORTC.  This allows for varied resource allocation depending on the other I/O used.  If PORTC is completely free, it can be used as a full 8-bit I/O port.  Otherwise SPI can be used.

 

The first board I built out has the headers, and a Beau Interconnect (now Molex) terminal block socket with detachable screw terminals socket.  The second board built has dedicated screw terminals and no headers for a cleaner look.

 

If you look closely, you can see the green wire work done on the first board due to me stripping a pad of one of the capacitors while trying to replace an incorrect value capacitor.  And I originally built the first one with a 4MHz crystal before reading the datasheet and realizing a 12MHz or 48MHz crystal are the only ones that work for USB with this cpu.  I was able to remove the wrong crystal using two soldering irons, and then replaced it with the 12MHz crystal after another order from Digi-Key.

 

Next step is to load these with the Microchip USB HID bootloader, write up some documentation, and start selling some on eBay.

USB RS-485 Adapter Through Hole PCBs

Here is my first PCB design that has gone to production. I redid the schematics of my original design now implemented in Eagle and also did a two layer PCB layout. I used Seeed's PCB service to produce the PCBs, ordered parts from Digi-Key and assembled them by hand. There were two mistakes with the board. Somehow I didn't connect VCC from USB, and inadvertently connected VCC to VUSB. Three cuts and three jumpers later and the boards work fine.